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THE RELATION OF TEMPERATURE AND HUMIDITY TO 
I INFECTION BY CERTAIN FUNGI 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the Degree of 

Doctor of Philosophy 



By 
JOHN IRVIN LAURITZEN 



Hrprlnted from PnYTOPATHOLOOY. Vol. IX 
January, 1910 



THE RELATION OF TEMPERATURE AND HUMIDITY 
TO INFECTION BY CERTAIN FUNGI 



A THESIS 

Presented to the faculty of the Graduate School 

of Cornell University for the Degree of 

Doctor of Philosophy 



By 

JOHN IRVIN LAURITZEN 



Reprinted from Phytopathology, Vol. IX, No. 1, 
January, 1919. 



<•#' 



L 3 






Reprinted from Phytopathology, Vol. IX, No. 1, January, 1919 



THE RELATION OF TEMPERATURE AND HUMIDITY TO 
INFECTION BY CERTAIN FUNGI 1 

J. I. Lauritzen 
INTRODUCTION 

Very early in the history of plant pathology a fundamental relation be- 
tween weather and plant diseases was recognized, not only by the pa- 
thologist but by the farmer. Even before anything was known about the 
nature of diseases, the weather was thought to have an intimate connec- 
tion with their causes, and by many to be responsible for their production; 
and yet very little work has been done to analyze the exact manner in 
which weather conditions affect diseases or disease production, except in 
an observational way. 

The effects of temperature, humidity, rainfall, and dew have not been 
isolated, except in a few cases, and then chiefly from observation or under 
partially controlled conditions. Never, so far as the author is aware, has 
the influence of temperature and humidity upon infection been studied 
separately where both have been under control. 

The importance of taking cognizance of the one while studying the 
other in connection with any growth phenomenon will be emphasized from 
the following examples of the influence of temperature and humidity on 
the growth of bamboo. Shibata (28), working under field conditions in 
Japan, gives a table which indicates a close relation between the daily 
growth of bamboo and temperature (16°C. to 20°C.) and scarcely any re- 
lation to humidity. Lock (19), working at Peradeniya, on the other 
hand, found that the daily growth depends largely upon the water supply 
and the moisture content of the air, and has little relation to the tempera- 
ture, which in his experiments fluctuated beween 19° and 26°C. 

The difference in the temperature of the two places will account for the 
seeming discrepancy, as far as the temperature is concerned. At Pera- 
deniya the temperature is apparently the optimum for the growth of bam- 

1 Also presented to the Faculty of the Graduate School of Cornell University, 
March, 1916, as major thesis in partial fulfillment of the requirements for the 
degree of doctor of philosophy. The writer is indebted to Dr. Donald Reddick and 
Dr. V. B. Stewart under whose immediate direction the work was performed for 
valuable assistance and suggestions in connection with the investigation and in the 
preparation of the manuscript. 



8 Phytopathology [Vol. 9 

boo, and covers a range of several degrees, while in Japan it falls below 
the optimum, consequently the growth curve follows closely that of the 
temperature. A comparison of the humidity of the two regions, as far as 
a comparison is possible from the data that are available, reveals very 
little difference in the moisture content of the air. It is apparent that 
this humidity, which varies largely between 70 per cent and 90 per cent 
influences the amount of growth under the favorable temperature at Pera- 
deniya. Its influence is evidently obscured by the unfavorable tempera- 
ture in Japan. Whether the humidity can become so unfavorable as to 
obscure the effects of temperature is not known from the data at hand, 
but it is probable. One thing seems certain, however, that in studying 
either of these factors one cannot afford to ignore the one while the other 
is under observation; in fact, it would be preferable to hold one of these 
factors constant when observing the other. 

In earlier work in pathology a clear distinction has not been drawn 
between the infection period and the period of incubation. 2 Such a dif- 
ferentiation is not always possible, and perhaps it is never possible to 
state definitely the exact point at which the infection period ends or the 
period of incubation begins. However, in most cases they can be sepa- 
rated sufficiently to study each apart from the other. Considerable work 
has been done to show the influence of temperature on the production and 
development of disease, but the two periods have been studied con- 
jointly. Less work has been done upon the relation of humidity to this 
phenomenon but a sharper separation has been made between the infec- 
tion and incubation periods. 

Balls (4) conducted temperature-infection experiments with Rhizoc- 
tonia (Corticium vagum B. and C, var. Solani Burt) on cotton (Gossyptum 
spp.) in which he found that infection took place and became evident in 
twenty-four hours at a temperature of 20°C. At 33°C. no infection oc- 
curred. Here the infection and incubation periods are crowded into such 
a short space of time and apparently so fused together that probably it 
would be difficult to separate them. The experiments were conducted by 
placing mycelium of the fungus in contact with seedlings placed upon 
several layers of moist filter paper in a petri dish, which in turn was placed 
in an infection chamber. 

Gilman (11) performed some soil infection experiments with Fusarium 
conglutinans Wollenw. on cabbage (Brassica oleracea L.) which are of inter- 
est in this connection chiefly because he worked in a greenhouse in which 
the temperature was automatically controlled. He also conducted some 

2 Infection period as here used is the period during which the pathogen penetrates 
the host until it becomes established with the host. Incubation period is the period 
of development that follows until the symptoms of the disease become visible. 



1919] Lauritzen: Infection Relations 9 

experiments in a glass infection chamber where the temperature was con- 
trolled by an electric thermo-regulator. The difficulty of studying in- 
fection apart from the incubation period is here apparent. It is not, 
however, so important in this instance that they should be studied sep- 
arately, because the environmental factors are not so variable except in 
the case of temperature. 

Tisdale (29) studied the infection of flax by Fusarium Lini Bolley. He 
found that the lower temperature limit for infection was about 15°C, and 
makes the statement that most of the infection occurs between 20° and 
30°C. The temperature was controlled in one set of experiments by em- 
ploying positions at different distances from a radiator in a green house, 
in another by means of a cii dilating water jacket about the plant con- 
tainers. He also investigated the influence of temperature upon the growth 
of the fungus in culture media, and determined the limits to be 10° and 
37°C. with an optimum temperature at 26° to 28°C. 

Johnson (14), in working with Thielavia basicola Zopf. to test the range 
of parasitism on a large number of plants, controlled the moisture content 
of the soil and recorded the soil and air temperatures. The temperature 
of the air and soil depended upon greenhouse conditions. 

Fromme (10) was unable to produce infection on oats (Avena sativa L.) 
by Puccinia coronifera Kleb. with a relative humidity of 75 per cent to 80 
per cent and a temperature of 55° to 85° F. He conducted an experiment 
designed to determine what conditions of humidity were necessary for 
infection. He grew his plants in an open case made of window sashes 
where the humidity averaged 93 per cent with a variation of about 2 
per cent to 3 per cent. Although he inoculated thoroughly, he obtained 
only slight infection. In an experiment where one pot was covered and 
another stood in an open box there was an average of 161.6 lesions per 
plant in the first case as compared with 10.4 or 6 per cent in the latter. 

Some interesting results were obtained by Levin (17) in connection with 
an experiment planned to determine the time required for the infection 
of tomatoes (Lcyoporsicum escidentum Mill.) by Septoria lycopersici Speg. 
He sprayed ten plants with a water suspension of spores, placing 9 of them 
in a Wardian case, where a high humidity was maintained by means of a 
fine spray of water. A plant was taken out at intervals of 6, 12, 24, 36, 
48, 60, and 72 hours and dried immediately by an electric fan and placed 
in an open window until infection became evident. After a lapse of five 
days all the plants, including the one left on the outside, showed charac- 
teristic lesions of the disease. This experiment was repeated in detail, 
except that the plants after inoculation were exposed to a current of air 
from an electric fan until the disease appeared. The results were similar 
to those secured in the previous experiment. Infection was also obtained 
by applying dry spores. 



10 Phytopathology [Vol. 9 

From the results of these experiments the author concludes that it is 
questionable whether a film of water over the plant surface for at least a 
number of hours is essential to infection. 

The purpose of the present study is to determine the influence of tem- 
perature and humidity upon infection, and to find out whether a film of 
water covering the surface of the plant is essential for the fungus to become 
established upon the host. 

APPARATUS 

The apparatus consists of two double chambers with thermo-electric 
connections to furnish heat, and power to run fans. The outer chambers 
are 40 by 54 by 48 inches in size and are made of glass. The inner are 11 
inches smaller in each dimension and so placed that there is an air space 
of 5 inches on all sides. They are constructed of wood except the lids, 
which are of glass and slope at an angle of 40° from the horizontal. The 
wood portion is coated on the inside with paraffin of a high melting point 
to prevent the absorption of water. Both inner and outer chambers are 
provided with heating coils and thermostats. In the latter case a relay 
was employed to prevent sticking of the thermostat, which was occa- 
sioned by the use of larger wire necessitated to produce the required heat 
for the outer chamber. 

The evaporation surface for the control of the humidity was supplied 
by open pans containing either pure water or saturated salt solutions. The 
humidity was read directly from psychrometers upon which was directed 
a constant current of air from a fan. 

FACTORS 

In approaching any physiological problem one is confronted with cer- 
tain difficulties. One of these is the isolation of the particular factor to 
be studied. The conditions affecting physiological processes are not only 
numerous, but complex, and sometimes so interrelated as to make their 
separation impossible. 

The usual procedure is to hold all the other factors constant in order to 
get at the facts of the particular one to be observed. Having thus reduced 
the problems to simple terms, one might think he could proceed directly 
to the solution of his problem, but he soon finds that the procedure is not so 
simple. One should not only have the conditions constant, but they should 
be at their optimum, and such an accomplishment is by no means easy, 
if indeed possible, with our present knowledge of the nature of physiologi- 
cal processes, the factors affecting them, or methods of investigation. 

In the present study an attempt has been made to keep the known and 
possible factors affecting infection constant as far as possible with the 



1919] Lauritzen: Infection Relations 11 

means accessible. An attempt has been made to control, in part, condi- 
tions influencing the growth of the host plant, such as the fertility, physi- 
cal properties, organic matter and water content of the soil, light, tem- 
perature, and humidity. The first four of these conditions are fairly easy 
to control; the latter three involve more difficulties. Temperature and 
humidity have been controlled as far as is possible under greenhouse con- 
ditions. Light is the most variable factor and no attempt has been made 
to control it. The greatest difference in light is between summer and 
winter. Whether this difference is sufficient to alter the susceptibility of 
the host plant to the attack of the fungus, or in any way influences the in- 
fecting ability of the fungus, is not known. No such influence has been 
noticed in the present experiments. It would seem that influences of 
light become less important when making comparison between the suc- 
cessive periods required for the growth of the plants while they attain 
sufficient size for inoculation purposes. 

Temperature and humidity may affect each plant differently, which of 
course is true of the other factors. The exact range of temperature and 
humidity favorable for the growth of the plants employed in these experi- 
ments has not been determined. A variation in the range with the plant 
is, however, generally recognized. It would have been desirable to have 
grown these plants under optimum conditions, but these conditions were 
not available, besides the optimum for each of these plants is not known. 
These same conditions also come into operation during the incubation 
period. 

Light as it exists under greenhouse conditions is not known to be a 
factor. Since light under natural conditions is not usually regarded as the 
limiting factor in photosynthesis, upon which host and parasite alike 
largely depend for their organic nutrition, it would seem that the reduc- 
tion in food due to the reduction in light under greenhouse conditions would 
not be sufficient to alter the number of infections more than slightly, if 
at all. 

. It would seem reasonable to assume that temperature and humidity 
during the incubation period do not influence the total number of infec- 
tions if sufficient time is allowed for the viable spores to establish a rela- 
tion with the host. It is possible that the border-line temperatures and 
humidities might cause a variation in the susceptibility of the host to the 
parasite. There is some evidence to support this position in the case of 
temperature. 

Ravn (25), in studying the influence of temperature upon the infection 
of barley by Helminthosporium, found that the incubation period was 
forty-eight hours in a warm greenhouse as compared with seventy-two 
hours in a cold house. The total amount of infection was slightly in favor 



12 Phytopathology [Vol. 9 

of the cold house. Fifteen out of 16 plants were infected in the cold 
house, while 12 out of 15 in the warm house were infected. He concludes 
from this experiment that temperature does not alter the total amount 
of infection. 

Fromme (10) obtained similar results with Puccinia coronifera on oats. 
Plants inoculated and grown at a temperature ranging from 20° to 30°C. 
showed evidence of infection on the fourth day, while plants inoculated 
at the same time and grown in a greenhouse at a temperature varying- 
between 14.5° and 21°C. showed indications of the disease only after seven 
days. This experiment was repeated with similar results. There was a 
slight difference in time due to a difference in temperature, but the varia- 
tion was in the same direction. The degree of infection was not, however, 
different in the two cases. 

It seems in the foregoing cases that the temperature employed, whether 
high or low, was sufficiently favorable to permit of the maximum amount 
of spore germination, or at least these temperatures allowed about the 
same percentage of germination; otherwise there would be a difference in 
the number of infections, unless we assume an alteration in the capacity 
of the fungi to cause infection or of the hosts to resist it. The latter seems 
less feasible because it would be a remarkable coincidence if there should 
be a shift of virulence or susceptibility in such an exact ratio that we 
would have the same number of infections even though there were a shift 
in the percentage of germination, especially when we are dealing with 
two different host plants as well as two pathogens. 

Mains (20) by altering the humidity during the incubation period 
obtained more infection on corn by Puccinia sorghi Schw. under high 
humidity than under low. He employed only 12 hours as an infection 
period and it is possible that there would have been more infection 
where the plants were under low humidity had the infection period been 
extended. 

CONDITIONS AFFECTING THE INFECTION PERIOD 

The light in the infection chamber was much reduced. First, because 
the inner chamber was partially constructed of wood; second, the light that 
reached the plants passed through two panes of glass; and third, the source 
of light was the diffused light of the headhouse. (It would have been de- 
sirable for the inner chamber to have been of glass, but such a chamber 
was not available.) Whether this subdued light for a period of twelve 
hours was sufficient to alter the relation of host and parasite can not be 
stated from our present knowledge. It would be expected to affect the 
host more than the parasite, because of the autotrophic character of the 
host. Furthermore if this diffused light had any effect in the short 



1919] 



Lauritzen: Infection Relations 



13 



period of time during which the plants were in the infection chamber it 
would be to reduce the photosynthetic processes. The reduced food would 
probably affect only the last stages of infection, after the germ tube had 
penetrated the host and the energy of the spore was exhausted or reduced. 
On the other hand the assumption might be made that there is an altera- 
tion in the susceptibility of the host, due to a disturbance of an osmotic 
or chemical equilibrium. The usual time required for starch to be re- 
moved from the plant in total darkness seems to indicate that there would 
be no actual food shortage. 

table i 
Record of infection in total darkness as compared with the light of the headhouse in case 



of bean and buckwheat and the greenhouse in case 


of wheat 






LIGHT 


DARKNESS 








Plants 
infected 


Plants 
wilted 


Plants 
infected 


Plants 
wilted 


REMARKS 


July 27, 1917 


Benin 


3-3 


3-3 


3-3 


3-3 


\<> apparent differ- 
ence 


July 28, 1917 


Bean 


3-3 


3-3 


3-3 


3-3 


No difference 






Plants 
infected 


Total 

number 

of 

spots 


Plants 
infected 


Total 

number 

of 

spots 




August 6, 1917 


Buckwheat 


3-3 


28 


3-3 


28 


The number of 


August 28, 1917 


Buckwheat 


3-3 


300 


3-3 


250 


plants infected 
and the number 
of spots are the 
criteria for the 
amount of infec- 
tion 


February 24, 1918.. . . 


Buckwheat 


3-3 


230 


3-3 


295 


Under plants in- 


January 25, 1918 .... 


Wheat 


23-24 




19-21 




fected 3-3 indi- 


January 28, 1918 .... 


Wheat 


13-14 




13-14 




cates that three 
out of three plants 
were infected 



Some experiments (table 1) were conducted to show whether total 
darkness as compared with the light of the greenhouse in one case and the 
light of the headhouse in two other cases alters the total infection of the 
host plants employed, under the conditions of the experiments. The 
following pathogens and host plants were used in the experiments: Col- 
letotrichum lindemuthianum (Sacc. & Magn.) Bri. and Cav. on bean (Pha- 
seolus vulgaris L.); Ascochyta fagopyrum Thuen. et Boll, on buckwheat 
(Fagopyrum esculentum Moench.) ; Puccinia graminis Pers. on wheat (Tri- 
ticum sativum Lam.). Both the bean and buckwheat experiments were 



14 Phytopathology [Vol. 9 

conducted in the headhouse mentioned above. In each experiment three 
plants were placed under a bell jar covered with black paper and three 
under a jar not so covered. The jars stood on a table before a window. 
The reason for using the headhouse instead of the greenhouse was that in 
the latter, during the time in which the experiments were running, the sun- 
light became so intense at times that under the high humidity of the 
bell jars the plants were liable to injury. The wheat experiments were 
performed in the greenhouse during the winter months when the sunlight 
was not so intense; in fact, cloudy weather prevailed most of the time. 
The other conditions of the wheat experiments were the same as those 
mentioned above except that there were more plants used. The experi- 
ments were repeated in each case and were run for twenty-four hours, 
after which the plants were removed to the greenhouse, where they re- 
mained until infection became evident. The temperature range was largely 
between 70 and 80° F. The results are represented in table 1. 

It seems fairly safe to conclude from these experiments that light in 
the infection chamber is not a limiting factor in case of the plants used. 
It is possible, however, that at the border temperatures and humidities 
light may manifest itself as a limiting factor. 

The carbon dioxide relation 

When plants are placed in a closed chamber there is an accumulation of 
carbon dioxide whenever it is not used up by photosynthesis. The extent 
of this accumulation depends upon the tightness of the chamber and the 
amount of circulation provided. The question arises as to whether the 
concentration of the carbon dioxide becomes sufficiently great in the in- 
fection chamber to become deleterious to the host and parasite. If there 
is an injurious effect, it is possible that the effects are the same in both 
host and parasite, in which case there probably would be no change in 
the number of infections. There would be a greater accumulation of 
carbon dioxide at the higher temperatures, at least until the optimum for 
respiration was reached, and consequently the effects would be more seri- 
ous than at low temperatures. 

The chambers were not perfectly air-tight. This was indicated by the 
fact that whenever the electricity was cut off from the heating coils the 
fall in temperature was sufficiently rapid to show some interchange of 
air between the inside and outside of the chamber. The greater the dif- 
ferences in temperature on the inside and outside, the greater would be 
the exchange consequently the tendency for accumulation of C0 2 at high 
temperatures would be compensated for (at least in part). It would 
seem therefore that the source of error from carbon dioxide injury would 
be slight if not negligible. 



1919] Lauritzen: Infection Relations 15 

Influence of sudden change of temperature 

When the host plant and pathogen are introduced into the infection 
chamber they are subjected to a more or less sudden change of tempera- 
ture, especially when working at low temperatures. 

A number of investigators have studied the influence of a sudden change 
of temperature upon growth in flowering plants, with contradictory results. 
Sachs (26) and Pedersen (22) conclude that the growth curve follows 
closely that of temperature. Koeppen (15), Askenasy (3), True (30), 
Price (23), and Lehenbaur (16) claim that the change itself has a tem- 
porary effect, the time varying from one-half to three hours, depending 
upon the investigator and the amount of change. The evidence seems to 
be in favor of the latter conclusion. How much this temporary effect 
may influence infection is not known. Eriksson (9) exposed aeciospores 
of Puccinia graminis to a temperature of 3°C. for two hours and then 
raised the temperature to about 20°C. He claims that such a change has 
a beneficial effect and increases the percentage of germination. Melhus 
(21) found that intermittent temperatures, whether changing from high 
to low or vice versa, tend to slightly check germination, but suggests that 
the small variation may be due to experimental error. 

Duff (6) found that urediniospores of Cronartium ribicola F. de Wal. 
(which become less viable with age and lose their power of germination *in 
four weeks) which were placed in a refrigerator two weeks after collection 
germinated only in a small percentage, but a reduction in temperature 
stimulated a large increase in germination. Spores subjected to a sudden 
change of temperature three weeks after being collected were stimulated 
to a slight degree to germinate. 

The control of temperature and humidity 

On the whole, with the size of the chambers employed the temperature 
can be kept within a variation of 1°F. The constancy of the tempera- 
ture is greatly facilitated by the double chamber arrangement with two 
heating systems and by the use of fans both in the inner and outer 
chambers. 

The temperature control was limited by outside conditions. The cham- 
bers were situated in a potting room of a greenhouse where it was possible 
to maintain a fairly low uniform temperature during the winter. The 
temperature of the room could be altered by ventilation and the use of 
steam radiators. This arrangement was sometimes convenient when 
working at higher temperatures. 

The control of humidity was accomplished by means of open pans of 



16 Phytopathology [Vol. 9 

water or saturated salt solutions in combination with temperature 
manipulations. 

Humidities above 95 per cent were difficult to attain whenever the tem- 
perature on the inside of the chambers was much higher than that of the 
outside air, because of inequalities in temperature in the outside chamber. 
This difficulty was partly overcome by the use of an electric fan and by 
placing beakers of water on the heating coils. A device was developed 
during the later stages of the investigation by which it was possible to 
maintain a saturated condition of air. Instead of using the air heating 
coils as a source of heat a water heating coil was placed in an evaporating 
pan containing water, thus insuring a slightly higher temperature of the 
evaporating surface than of the air and consequently a saturated 
atmosphere. 

Whenever a lower humidity than 95 per cent was desired saturated salt 
solutions were used. An excess of salt insured a definite vapor pressure 
at a given temperature and hence a constant humidity. The wide range 
of vapor pressure of saturated salt solution made it possible to obtain 
almost any humidity desired. 

It is not possible to predict the exact humidity that will result from a 
given saturated solution. First, because the vapor pressure of the ma- 
jority of saturated solutions has not been worked out for the various tem- 
peratures; second, the vapor pressure of the entire system is altered by the 
introduction of plants. The leaf surface presents an evaporating surface 
very near that of pure water, tending to increase the humidity of the 
system. However, as soon as the system comes to an equilibrium, the 
bumidity becomes constant. It is possible by the inspection of the vapor 
pressure of the various salts at a given temperature to predict what salt 
to employ in order to obtain an alteration in humidity in the desired direc- 
tion. The humidities obtained from the various salts vary in the same 
direction as the vapor pressures of those salts. Some of the salts-used are 
as follows: — Potassium sulphate with a vapor pressure of the saturated 
solution of 17.21 mm. mercury at 20°C, Barium chloride V.P. at 20°C. 
15.45, Sodium nitrate V.P. at 20°C. 13.7 mm., Cadmium chloride V.P. at 
20°C. 12.2 mm. 

Relative humidity as a unit of comparison 

As has been pointed out by Livingston and others, relative humidity 
is not a satisfactory unit of comparison whenever more than one temper- 
ature is employed. Livingston (18) suggests the use of vapor pressure 
deficit, which equals the difference between the maximum vapor pressure 
of water vapor at a given temperature and the actual pressure of water 
vapor in a given space at a given temperature. 



1919] Lauritzen: Infection Relations 17 

methods and materials 

The following pathogens and host plants were employed in these ex- 
periments: Collectotrichum lindemuthianum (Sacc. & Magn.) Bri. & Cav. 
on red kidney bean (Phaseolus vulgaris L.) Puccinia graminis Pers. var. 
tritici Erick on wheat (Triticum), and Ascochyta fagopyrum on buck- 
wheat, gray variety , (Fagopyrum esculentumMoench.) . The fungi employed 
were all pure line strains to which the respective hosts were susceptible. 
An attempt was made to secure pure line strains of the host but this 
could not be done except in the case of wheat. 3 

The bean and buckwheat plants were grown in two inch pots and the 
wheat in an inch and a quarter pots in a greenhouse with a temperature 
ranging from 60° F. to 85° F. and relative humidity varying from 60 per 
cent to 85 per cent. 

Plants of the same age were used as far as possible. Some variation 
was inevitable, however, even under greenhouse conditions. The beans 
were usually from sixteen to twenty days old, the wheat from seven to 
ten, and buckwheat from twenty to twenty-four days old. An effort was 
likewise made to use spores of the same age. Here some variation oc- 
curred, due to the necessarily different conditions under which the organ- 
isms were grown. Colletotrichum was grown on bean pods, Ascochyta on 
potato agar, and the spores of Puccinia graminis obtained directly -from 
pustules on the host plant. 

Twenty pots were used in each experiment, with one plant in each pot, 
except in case of wheat, where the number of plants varied from three to 
five. These cultures were divided into five series of four pots each and 
designated by the following symbols: Ch 1, Ch 2, Ch 3, F, and D. The 
plants in Ch 1 were taken directly from the greenhouse when the particu- 
lar experiment was started, and placed in the infection chamber. The 
purpose of this series was to show whether or not any infection that oc- 
curred was due to spores that may have come in contact with the host 
before inoculation. The remaining four series were sprayed with a spore 
suspension from an atomizer (except in case of wheat) and used as fol- 
lows. The plants in Ch 2 were placed in a special chamber at tempera- 
tures and humidities known to be favorable for the development of the 
disease. This procedure was to deteimine whether the spores were viable 
and whether infection would take place if conditions were favorable. 
The plants of Ch 3 were dried immediately by means of an electric fan 
and left in the greenhouse as a check to show whether infection occurred 

3 The wheat seed for these experiments was furnished by Dr. E. C. Stakman. 
This strain was given the number 169 by him and was used because of its suscepti- 
bility to the attack of Puccinia graminis. 



18 



Phytopathology 



[Vol. 9 



in the infection chamber or in the greenhouse. Series F consisted of plants 
placed in the infection chamber directly after inoculation and covered 
with a water suspension of spores. In series D the plants were dried at 
once and placed in the infection chamber. This series was employed to 
determine whether a film of water over the surface of the plants was es- 
sential to infection. Sometimes series D was omitted in the temperature 
experiments. 

TABLE 2 

Record of amount of infection on wheat plants by Puccinia graminis tritici at various 
low temperatures, the humidity being practically constant 





ULATION 


PSYCHROMETER 

READINGS 

FAHR. SCALE 


DEPRES- 
SION OP 
WET 
BULB 


RELA- 
TIVE 
HUMID- 
ITY 


EXTENT OP 


INFECTION 




Fi 


Ch.li 


Ch.2' 


Ch.3' 




Number 

of 

plants 

infected 


Number 

of 
plants 
infected 


Number 

of 
plants 
infected 


Number 

of 
plants 
infected 


December 18, 


1917 


53.0-52.6 


0.4° 


97.5 


12-34 2 


0-17 


17-18 


0-16 


December 19, 


1917 


53.0-52.6 


0.4° 


97.5 


8-28 


0-20 


14-24 


0-16 


December 31, 


1917 


52.7-52.2 


0.5° 


97.0 


9-43 


0-24 


22-25 


0-16 


December 21, 


1917 


51.7-51.2 


0.5° 


97.0 


23-43 


0-18 


16-22 


0-20 


January 3, 


1918 


50.8-50.4 


0.4° 


97.0 


2-30 


0-15 


18-22 


0-14 


January 10, 


1918 


49.8-49.75 


0.05° 


99.0 


5-44 


0-18 


19-20 


0-17 


December 10, 


1917 


47.2-46.7 


0.5° 


96.0 


0-30 


0-16 


16-19 


0-12 


January 6, 


1918 


47.1-46.75 


0.35° 


97.0 


2-44 


0-16 


19-20 


0-16 


December 11, 


1917 


47.0-47.0 


0.0° 


100.0 


1-40 


0-20 


17-25 


0-22 


January 19, 


1918 


46.85-46.75 


0.1° 


99.0 


1-41 


0-22 


25-35 


0-22 


January 22, 


1918 


46.48-46.2 


0.28° 


98.0 


7-35 


0-16 


27-27 


0-16 


January 21, 


1918 


45.5-45.3 


0.2° 


98.04- 


5-31 


0-17 


12-24 


26 


December 14 




42.2-42.0 


0.2° 


98.04- 


0-38 


0-20 


23-23 


0-14 









1 An explanation of symbols is given on page 17. 

2 In this table the number of diseased plants is the criterion of infection. 12-34, 
0-17, 17-18, 0-16, etc., means that 12 out of 34 plants, out of 17, etc., were infected. 

The wheat was inoculated by removing the spores from pustules of 
diseased leaves by means of a scalpel and spreading them on the wheat 
leaves. Ch 2 and F were then sprayed with water from an atomizer. 

The plants were allowed to remain in the infection chamber for twenty- 
four hours and were then returned to the greenhouse, where they remained 
until the disease developed. The time for the development of the dis- 
ease varied somewhat with the greenhouse conditions, but since the time 
is influenced little during the infection period it was not considered in 
recording data. Sufficient time was allowed in each case for any possible 
infection to become manifest. Bean plants were allowed ten to fourteen 
days, wheat thirteen to twenty, and buckwheat ten to fifteen days. 



Ml II 1 1 i «r»»»rgnt 



1919] 



Lauritzen: Infection Relations 



19 



An electric fan was placed in the greenhouse in such a position as to 
blow a current of air between and above the plants in order to prevent 
the accumulation of higher humidities immediately around the plants. 
This procedure was found necessary in some instances to prevent infection 
of buckwheat. The bean and wheat never showed any tendency to the de- 
velopment of the diseases in the greenhouse. In one instance Ch 3 plants 
showed infection in case of wheat. 

TABLE 3 

Record of infection on buckwheat plants by Ascochyta fagopyrum at various low 
temperatures, the humidity remaining practically constant 





PSYCHROME- 
TER READINGS 
FAHR. SCALE 


m 
►j 
& 
m 

Eh 
W 
i* 

o 
o 

GO 
CO 
H 
K 
Ph 

h 

a 


J- 

E* 



s 
t> 
w 

H 

> 

< 
J 
H 

X 


EXTENT OF INFECTION 1 




F 


Ch. 1 


Ch. 2 


Ch. 3 


DATE OP 
INOCULATION 


— 

"c. 

3.2 


CD 

S 

2 °> 

c e 
^_ o 

cS'S 

ts 


"E 

CD "^ 

11 


c 

"ft 
'o-ri 

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3.5 

iz; 


CD 

s 
£■« 

c a 
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oJ'S 

"o — 

H 


c 
J5 

t. CD 
CD "t> 

3.S 


December 21, 1917 


59.50-59.15 


0.35° 


98.0 


7-8 


52 


0-4 


4-4 2 


Numerous 


0-4 


December 22, 1917 


56.70-56.10 


0.6° 


96.0 


0-8 





0-4 


4-4 3 


43 


0-4 


December 19, 1917 


56.10-55.40 


0.7° 


95.5 


2-9 


4 


0-4 


4-4 


55 


0-4 


January 14, 1918... 


54.25-54.18 


0.07° 


99. C 


1-8 


1 


0-4 


4-4 


60 


0-4 


January 7, 1918. . . 


53.25-53.00 


0.25° 


98.5 


1-8 


1 


0-4 


4-4 


20 


0-4 


December 11, 1917 


48.40-48.00 


0.4° 


97.0 


0-8 





0-4 


4-4 


32 


0-4 


January 22, 1918... 


46.48-46.1 


0.38° 


97.0 


4-8 


15 


0-4 


4-4 


100 


0-4 


January 21, 1918... 


45.60-45.35 


0.25° 


98.5 


1-8 


3 


0-4 


4-4 


150 


0-4 


December 13, 1917 


42.80-42.60 


0.2° 


98.5 


0-8 





0-4 


4-4 


Numerous 


0-4 


December 10, 1917 


41.70-40.65 


1.05° 


92.0 


0-6 





0-4 


4-4 


36 


0-4 


December 14, 1917 


38.00-37.80 


0.2° 


98.5 


0-8 





0-4 


4-4 


All dead 


0-4 



1 Two methods of measuring the amount of infection are employed in this table, 
for example, in column 1 under F the number of diseased plants is used as a basis, 
while in column 2 the total number of lesions occurring on all the plants marked F 
are given. 

2 All plants were wilted. 

3 Infection on primary leaves only, 3 plants wilted, one leaf of remaining plant 
wilted. * 



Influence of low temperature upon infection of wheat 

From table 2 it will be seen that wheat can become infected by Puccinia 
graminis at a temperature as low as 45.5° F. but the infection is very 
slight and rapidly decreases at temperatures below 45.5° F. In the single 
experiment run at 42° F. there was no infection. This experiment should 



20 



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1919] 



Lauritzen: Infection Relations 



21 



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22 Phytopathology ' [Vol. 9 

at least have been duplicated but the low temperature did not prevail at 
the time. However, the humidity was very favorable and the infection 
between this point and 50° F. was very slight. It seems therefore that 
45° F. is near the lower limit of infection. This point is only about 9° F. 
above the lowest temperature at which Johnson (13) was able to obtain 
germination of spores of Puccinia graminis. 

The amount of infection rises rapidly from within a few degrees of the 
lower limit to almost a fair average for the higher temperatures, indicating 
that there is no definite optimum temperature for infection. These results 
correspond to those obtained by Johnson (13) for germination of spores 
of Puccinia graminis. He found no definite optimum temperature when 
percentage germination was used as a basis for measuring the amount of 
germination. 

Influence of low temperatures upon infection of buckwheat by Ascochyta, 

fagopyrum 

No infection was obtained in buckwheat below 45.5° F (table 3). An- 
other experiment at 42° F. and at high humidity should have been con- 
ducted as a further check upon the lower limit but the outside temperature 
was not sufficiently low to do so. Some variation in the amount of in- 
fection between 45° F. and 59° F. will be noted, and even an absence of 
infection in some cases. An observation of a certain phenomenon in con- 
nection with spore germination of the pathogen suggests a possible ex- 
planation of this variation. At times, and for reasons unknown, the fun- 
gus produced one-celled spores. Whether these spores are merely imma- 
ture spores is not known, because old cultures sometimes contain them. 
These spores do not germinate nearly as well as the two-celled spores. 
At higher temperatures, however, they seem to produce infection. It is 
possible that these spores may fail to produce infection as the tempera- 
ture becomes less favorable. This problem needs to be solved. 

Low temperatures and infection of bean by C. lindemuthianum 

From table 4 it will be seen that the lower limit for infection of bean 
by Colletotrichum is 57° F. where the plants remain in the infection cham- 
ber for twenty-four hours. It is possible that if this time were extended, 
a lower limit might be obtained. 

The rise in the amount of infection here as in case of wheat and buck- 
wheat is rapid. Excellent infection was secured at 63° F. 



1919] 



Lauritzen: Infection Relations 



23 



Infection of wheat at higher temperatures by P. graminis tritici 

The highest temperature at which Puccinia graminis will produce infec- 
tion in wheat (table 5) is 80° F., at least under the conditions of the experi- 
ment. This temperature is 7.8° F. below the maximum at which the 
spores will germinate. It is possible that in a saturated atmosphere this 
temperature might be raised. It seems probable, however, that the 
highest temperature at which infection will take place is below the maxi- 
mum for germination. 

TABLE 5 

Record of infection on wheat plants by Puccinia graminis at various high temperatures, 
the humidity remaining practically const mi I 





PSYCH ROME- 


n 

p 
n 

H 
H 


at 

a 


EXTENT OF INFECTION 1 




F 


D2 


Ch. 1 


Ch. 2 


Ch. 3 




m , 


m i 




IB 1 




















+-> O 


DATE OF INOCULATION 


READINGS 


fe. 
O 


< 






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R£xs 


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0-4 


September 3, 1917 


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September 29, 1917 


78.0-77.00 


1.0° 


96.0 


1-5 


1-2 


0-4 


4-4 


0-4 



1 In these experiments the number of plants diseased was not counted (there be- 
ing 3 to 5 plants in each pot), but the number of pots in which infection occurred 
was used as basis of measurement. 

2 Explanation of symbols is given on page 17. 

Infection of bean at higher temperatures by C. lindemuthianum 

The highest temperature at which infection took place in bean was 
80° F. (table 6). With both wheat and bean a large number of experi- 
ments were run at temperatures above 80°. The increase in the number 
of plants infected was rapid as the temperature was lowered. The range 
covered is not sufficient to show the same decided increase in the amount 
of infection. One finds this suggestion, however, in the data. 

This maximum temperature for infection falls 7.8° F. below the tem- 
perature at which Edgerton finds Colletotrichum to grow in culture 
media. 



24 



Phytopathology 



[Vol. 9 






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1919] 



Lauritzen: Infection Relations 



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26 



Phytopathology 



[Vol. 9 



Infection of buckwheat at higher temperatures by Ascochyta fagopyrum 

The upper limit for the growth of buckwheat appears to be about 100° F. 
(table 7). Most of the plants collapsed after having been in the infection 
chamber at this temperature for twenty-four hours. Yet in one instance 
typical Ascochyta lesions appeared on plants that survived. I have ger- 
minated the spores of the fungus at a temperature of 106° F. The maxi- 
mum temperature for germination has not been determined. Some ex- 

TABLE 7 

Record of infection of buckwheat by Ascochyta fago-pyrum at various high temperatures 

and within the humidity range at which infection takes place 







pq 




EXTENT OF INFECTION 




F 


D 


Ch. 1 


Ch. 2 


Ch.a 






is 
























b 


^ 


B 


B 


«*H 


B 




PSYCHROME- 


a 










-^ 




o 




DATE OP INOCULATION 


TER READINGS 


o 

z 
o 


S 


a 


t* 


a 


h 


B 


a 


hi 


C3 




FAHR. SCALE 


w 

a 
> 


c 


xj 


o. 


42 


"ft 


a, 


J2 


a 








a 

3 m 

a a 


o-e 


^ B 


"o-a 
^■2 


hi 4> 


3 B 

fi e 


o-o 

a; -h> 






a 


H 


-° a 


_ o 


— o 


__ o 


■ss 


JJ tf 


_ o 










< 


in 


ca b 


a "2 

a.5 


cs m 


9.5 


3.5 


r. b 


3.5 






a 


« 


z 


H 


fc 


H 


£ 


£ 


H 


Z 






per 






















cent 


















March 12, 1918.... 


100.0-100.0 


0° 


100.0 


2-1 1 1 


2 


— 


— 


0-4 2 


4-4 


37 


0-4 


March 13, 1918.... 


100.0-100.0 


0° 


100.0 


0-8 3 





— 


— 


0-4 4 


4-4 


119 


0-4 


August 3, 1917 


97.7- 95.2 


2.5° 


91.5 


1-4 


Sev- 
eral 


1-4 


Few 


0-4 


4-4 


Nu- 
mer- 
ous 


2-4^ 


September 27, 1917 


93.3- 90.8 


2.5° 


91.5 


1-4 


1 


1-4 


3 


0-4 


4-4 


90 


0-4 


September 28, 1917 


92.6- 90.3 


2.3° 


92.0 


1-4 


5 


1-4 


2 


0-4 


4-4 


24 


0-4 


September 6, 1917 


91.0- 88.0 


3.0° 


89.0 


3-4 


10 


1-4 


2 


0-4 


4-4 


117 


0-4 



1 Four out of 11 plants were dead. Remaining were all injured. 

2 All 4 plants were dead at end of infection period. 

3 Seven out of 8 plants were dead. 

4 Two plants dead; 2 remaining plants injured. 

5 These plants show infection but they were at the end of the greenhouse, where 
there was dropping from the roof. 

periments were conducted at temperatures above 100° F., but the plants 
always died. 

The limits of temperature at which infection by Ascochyta occurred in 
buckwheat were wider than in wheat and bean. In the latter two the 
maximum temperatures for growth are higher than for infection. It is 
possible, at least in case of beans, to grow them at temperatures unfavor- 
able for the fungus and thus escape the losses due to this disease where 
the other conditions for its development are favorable. 



1919] 



Lauritzen: Infection Relations 



27 



Infection of buckwheat at various humidities by Ascochyta fagopyrum 

In table 8 is shown the infection of buckwheat at various humidities, 
the temperature remaining nearly constant. The lowest humidity at 
which infection has been observed to take place on buckwheat is 91 per 
cent. The humidity rises to 94.5 per cent where the plants were dried 
before placing them in the chamber. It will be noted, however, that con- 
siderable infection took place at this humidity. This table not only shows 
that infection can take place at the temperatures considered, within a 

TABLE 8 

Record of infection on buckwheat by Ascochyta fagopyrum at various humidities, the 
temperature remaining practically constant 





PSYCHROM- 


►4 

p 
n 
ft 
s 


H 


EXTENT OF INFECTION 




F 


D 


Ch. 

1 


Ch. 2 


Ch. 
3 




to 


•« 


to 


MH 


in 


to 






DATE OF INOCULATION 


ETER 
READINGS 


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& 




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CI 


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CO 


a 


a 

C3 


o 


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73 




P AH R. SCALE 






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November 15, 1917 


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November 20, 1917 


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57 


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November 13, 1917 


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2.0° 


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2 


0-4 





0-4 


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54 


0-4 


November 8, 1917 


78.7-76.9 


1.8° 


91.5 


0-4 





0-4 





0-4 


4-4 


100 


0-4 


November 27, 1917 


77.3-75.2 


2.1° 


90.6 


2-4 


4 


0-4 





0-4 


4-4 


55 


0-4 


October 4, 1917 


77.1-74.5 


2.6° 


89.0 


0-4 





0-4 





0-4 


4-4 


37 


0-4 


Octobers, 1917 


77.2-74.7 


2.5° 


89.0 


CM 





0-4 





0-4 


4-4 


46 


0-4 



1 Plant wilted (lesions not counted). 



range from 91 per cent to 100 per cent humidity, but that a film of water 
covering the leaf surface is not essential to infection. 

The question may arise as to the possible presence of a film on the leaf 
surface at such high humidities. It has been observed throughout these 
experiments that plants placed in the chamber with a film covering the 
leaf surface are dry when removed at the end of twenty-four hours. Since 
the chamber is always run at a temperature above that of the surround- 
ing atmosphere, evaporation must always take place because under these 
conditions saturation is rarely ever reached. The only cases where a 
condition of saturation has been observed are at the lowest temperatures. 



28 



Phytopathology 



[Vol. 9 



Infection of wheat at various humidities by P. graminis tritici 

The range of humidity for infection in wheat (table 9) is a little nar- 
rower than it is for buckwheat. The lowest humidity at which infection 
has been observed is 95 per cent. No infection takes place at 92 per 
cent and below. The same general difference is observed between the 
plants with a film and those without. The dry plants require a slightly 
higher humidity. 

TABLE 9 

Record of infection of wheat by Puccinia graminis tritici at various humidities, the 
temperature remaining practically constant 





PSYCHROME- 

TER READINGS 

FAHR. SCALE 


« 
j 
p 

n 

En 
H 

IS 

fc. 

O 

o 
35 

H 

IS 


H 

s 

a 
p 

a 

a 

> 

■<! 
J 
m 

« 




EXTENl 


' OF INFECTION 




F 


D 


Ch. 1 


Ch. 2 


Ch.3 


DATE OF INOCULATION 


en 

a 
'o-o 

<L> -^ 

■° o 
3.5 


00 

a 
a 

"ot3 
3.S 


"S 
"5 


in 

"3 

a 
"ft 

11 

3.5 


03 

a 
J3 
"a 

"o-a 

■- Q> 

I.S 

z 


February 18, 1918 

March 7, 1918 


70.0-69.6 
68.9-68.4 
68.2-67.3 
67.5-66.7 
68.9-67.9 
68.0-67.0 
68.0-66.5 
68.2-66.7 
68.5-67.0 
68.1-65.6 
68.0-65.3 


0.4° 
0.5° 
0.9° 
0.8° 
1.0° 
1.0° 
1.5° 
1.5° 
1.5° 
2.5° 
2.7° 


98+ 

97 

96 

96- 

95 

95 

93 

93 

93 

88 

88 


12-15 
5-22 
5-16 
8-19 
7-16 
6-17 
0-16 
0-15 
0-15 
0-20 
0-14 


15-17 
5-17 
2-19 
3-16 
3-13 
0-17 
0-15 
0-14 
0-15 
0-17 
0-16 


0-27 
0-26 
0-16 
0-20 
0-15 
0-18 
0-17 
0-12 
0-15 
0-18 
0-17 


22-22 
14-18 
10-15 
28-29 
10-11 
8-11 

12-17 
14-18 
12-16 
11-15 


0-25 
0-17 


March 8, 1918 


0-13 


February 24, 1918 

March 4, 1918 


4-24 1 
0-12 


March 10, 1918 


0-17 


November 17, 1917 

November 22, 1917 

November 28, 1917 

November 12, 1917 

December 3, 1917 


0-14 
0-14 
0-14 
0-19 
0-13 



1 In this case Ch 3 showed slight infection, the only case ever recorded on wheat. 

The temperatures at which the humidities were studied were arbitrarily 
selected, after considerable preliminary work. These temperatures were 
thought to be within the limits of the optimum. 



Influence of humidity upon infection of bean by Colletotrichum 
lindemuthianum 

The lowest humidity at which infection took place in bean is near that 
of wheat. The data in table 10 do not show any infection at 95 per 
cent humidity, but only one experiment was run at this humidity. Nega- 
tive results were also obtained with wheat at 95 per cent humidity. 



1919] 



Lauritzen: Infection Relations 



29 





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30 Phytopathology [Vol. 9 

A large number of experiments were run at humidities above 95 per 
cent. The data given in the table are representative of the results ob- 
tained. A large number of experiments were conducted at humidities of 
92 per cent and below. 

There is a rapid rise in the number and extent of infections from 95 
per cent up to 100 per cent. At 97 per cent humidity, the highest hu- 
midity given in the table, the amount of infection approaches closely that 
in Ch 2, where saturation was attained at least part of the time and where 
the film over the leaf was maintained throughout the infection period 
due to precipitation because of alterations in temperature. The tem- 
peratures in Ch 2 varied largely between 65° F. and 75° F. The same 
influence of the presence of a film is to be noted as in the wheat and 
buckwheat. 

DISCUSSION AND CONCLUSIONS 

Heretofore the study of the effects of temperature upon the relation of 
parasite to host has been limited largely to the influence of temperature 
upon the growth of the fungus and the germination of the spores. In a 
few cases the effects of temperature upon the development and extension 
of diseased tissue has been studied (Ball (4), Brooks and Cooley (5) ). 
This phenomenon is largely one of growth and seems to obey, in the main, 
the Van't Hoff law. The growth of the fungus behaves in the same way 
(Tisdale (29), Brooks and Cooley (5) ). 

A number of methods have been employed to measure the effect of 
temperature upon germination, with varied results. In some cases it 
would seem that all the factors involved were not considered. 

The extension of the germ tube and the development of mycelium have 
been used as a basis for the study of the influence of temperature upon 
germination and infection (Johnson, E. C. (13), Wiesner (30), Balls (4), 
etc.). Here one is dealing with a growth phenomenon, and when food is 
not a limiting factor one would expect the behavior of this phenomenon 
towards temperature to be the same as found among flowering plants and 
the growth of fungi in culture media. For every increase of 10°C. (within 
certain limits) there would be a doubling or trebling of growth in a given 
time (Tisdale (29), Brooks and Cooley (5), Edgerton (7) ). 

The time required for germination has been used as a measure of the 
influence of temperature. The results have been rather uniform, and 
there has been a general shortening of time with an increase of temperature 
to a more or less optimum temperature in the same proportion as de- 
manded by the Van't Hoff law (Anderson (1), Hecke (12), Wiesner (31), 
Ravaz (24), Melhus (21), Shapovalov (27)). Ames (2) obtained varied 
results with different species. In some cases the optimum is very broad, 



1919] Lauritzen: Infection Relations 31 

while in others the time is shortened with an increase of temperature to a 
rather definite optimum. 

Where percentage germination has been used as a criterion for measur- 
ing the effects of temperature, fairly uniform results have been obtained. 
The optimum, as a rule, is broad, as one would naturally expect if suf- 
ficient time were allowed at the lower temperatures for germination to 
take place. If a shorter time were used different results might be expected. 
Melhus' (21) results with the spores of Phytophthora infestans show a fairly 
broad optimum (5° to 13°C.) where he used the number of cultures in 
which germination occurred as a basis of measurement of the temperature 
effects. It is sharper, however, than that obtained by other investigators. 
Where he used the percentage germination in the various cultures as a 
criterion, there was a gradual rise in percentage from 5° to 13°C. He 
states, however, that there was a variation from 13 to 80 per cent in 
germination at the optimum. This fact may account for the difference in 
the two curves. Ames (2) abandoned percentage as a basis of measuring 
the effects of temperature upon germination because her results were not 
uniform. Anderson (1) found the percentage germination of the spores 
of Cylindrosporium scoparium Morg. was almost total between 12° and 
30°C, ranging between 95 and 100 per cent. Johnson (13) did not ob- 
tain a definite optimum temperature for Puccinia graminis by percentage 
germination, there being no uniformity between 9° and 25°C. 

From these results it would seem that the number of spores which 
germinate does not rise with an increase in the temperature to a definite 
optimum, but that the range at which a large number of spores will germi- 
nate is wide. One would expect, then, that there would be a wide range 
of temperature at which the number of infections that would take place 
would not vary much if sufficient time were allowed for the spores at lower 
temperatures to cause infection, providing some other factor did not enter 
in. This view corresponds to the results of the present experiments (tables 
2, 3, and 4). Some experiments were conducted between the tempera- 
ture limits given in the tables with results which conform to this conclu- 
sion. These results have also been confirmed by Ravn and Fromme 
(pages 11 and 12). 

An understanding of this phenomenon is important wherever the num- 
ber of lesions, such as in leaf spots, fruit spots, etc., is responsible for the 
chief loss due to diseases. If there were a definite optimum, the number of 
lesions that would develop would gradually decline as the temperature 
was lowered from the optimum. The infection phenomenon viewed in 
this light implies a different attitude towards control measures. Not 
only must the degree of temperature be considered, but the time to which 
the host plant is exposed to conditions of infection, in connection with 



32 Phytopathology [Vol. 9 

the number of infections that take place as well as the development and 
extension of a particular lesion. 

Some incidental data obtained in the present investigation in connec- 
tion with infection of bean by C. lindemuthianum near the lower tempera- 
ture limit indicate that the time element is important. The data point 
to a lower temperature limit for infection where forty-eight hours were 
used for an infection period than where twenty-four hours were used. 

From the data presented, an interesting relation between host and 
parasite is brought out. The temperature ranges for host and parasite 
are not identical in any of the cases. The temperature range for growth 
of bean and wheat is wider than for the germination of spores and of 
infection by C. lindemuthianum and P. graminis. The maximum temper- 
ature for infection by the two pathogens is about the same in the time 
employed (tables 5 and 6) while the lower limit for infection by P. gram- 
inis (compare tables 2 and 4) is lower than for infection by C. lindemu- 
thianum. The upper temperature limit for the growth of bean is higher 
than for germination of the spores of and infection by C. lindemuthianum f 
which fact has made possible the control of anthracnose in the Southern 
States. The optimum temperature for the growth of bean is probably 
higher than that of wheat. 

The exact temperature ranges for Ascochyta and buckwheat have not 
been determined. There is no indication as to which has the wider 
range. Their ranges do not coincide, because buckwheat is killed at a 
temperature at which infection takes place and below the maximum tem- 
perature for germination of spores of Ascochyta (table 7) . These relations 
are all important in connection with control measures. 

The variation in the amount of moisture in the air in different regions 
is probably important in the distribution of diseases over the earth's sur- 
face. The absence of certain diseases in semi-arid and arid regions where 
agriculture has been practiced for long periods of time may be due in part 
to the small moisture content of the air. 

Seasonal variation in the moisture content of the air plays an important 
part in determining the amount of disease that may develop. 

In the course of the present investigation (compare tables 8, 9, and 10), 
a variation in the humidity in the air required for infection for the indi- 
vidual plant has been exhibited. Infection occurred at a slightly lower 
humidity in buckwheat than in case of bean and wheat. As mentioned 
earlier, it was necessary to provide for circulation of air about the buck- 
wheat plants to prevent infection in the greenhouse. This same provision 
was found requisite in a few experiments conducted with Septoria lyco- 
persici Speg. on tomato. The tendency for infection to take place in the 
greenhouse was more marked with tomato than with buckwheat. 



1919] Lauritzen: Infection Relations 33 

The degree of humidity in the general environment of the plant may be 
an inaccurate criterion of the amount of moisture required for infection, 
at least when there is little air movement. The air movement created by 
an electric fan over a bench in the greenhouse has been sufficient to pre- 
vent infection of buckwheat by A.fagopyrum and of tomato by S. lycoper- 
sici where in its absence infection took place. The higher humidity in 
the immediate environment of the plant may be of considerable significance 
in connection with infection in nature. 

Just how the spore upon the plant surface obtains sufficient moisture 
for germination and infection is an unsolved problem. Within certain 
limits of humidity, that is, where the evaporation is not too great, the spore 
is able to absorb sufficient water for germination. The absorption may 
be from the host plant, at first by imbibition and later by osmosis. It is 
possible that in the depressions of the leaf surface and especially immedi- 
ately above the stomata a higher humidity prevails which may afford 
sufficient moisture for germination. 

There is a possible relation to hairiness because the juvenile leaves of 
buckwheat have more hair than the secondary leaves and seem to be 
infected more readily (the data contained in the tables are from the sec- 
ondary leaves). The secondary leaves of the bean are more pubescent 
and seem to be infected more easily at the limiting humidities. The hair 
would tend to prevent evaporation and increase the humidity at the leaf 
surface. 

SUMMARY 

The lower temperature limit for infection of wheat by Puccinia graminis 
tritici is somewhere near 42° F. The amount of infection rises rapidly 
and at 53° F. it approaches the average for higher temperatures. 

The lower temperature limit for infection of buckwheat by Ascochyta 
fagopyrum is about 45° F. There is some variation in infection between 
this temperature and 59° F., possibly due to the one-celled spores some- 
times produced in culture. 

The lower temperature limit for infection of bean by Colletotrichum is 
about 57° F. This limit may be influenced by the time the plants are in 
the infection chamber. 

The upper temperat re limit for infection of wheat is 80° F. 

The maximum temperature for infection of buckwheat by Ascochyta 
is about 100° F. At this temperature buckwheat plants are injured or 
killed. 

The upper temperature limit for infection of bean is 80° F. With the 
decrease of temperature there is a rapid increase in the number of plants 
infected. 



34 



Phytopathology 



[Vol. 9 



There seems to be no definite optimum temperature for infection in 
the hosts and parasites used where the number of infections is used as a 
measure of the amount of infection and sufficient time is allowed for the 
fungi to establish a relation with the hosts. 

The range of humidity for infection of buckwheat varies between 90 
per cent and 100 per cent. Where the plants are dried off before being 
placed in the infection chamber, it varies between 94.5 per cent and 100 
per cent. 

The humidity range for infection of wheat is between 92 per cent and 
100 per cent. The lowest humidity at which infection has taken place 
is 95 per cent. The range for the dried plants is a little narrower. 

The range of humidity for infection of bean lies between 92 per cent 
and 100 per cent. 

A film of water covering the leaf surface is not essential to infection. 

Bureau op Plant Industry, 
Washington, D. C. 

LITERATURE CITED 



(1 

(2 

(3 

(4 
(5 

(6 

(7 

(8 

(9 

(10 

(11 

(12 

(13 

(14 



Anderson, J. P. Rose canker and its control. Mass. Agr. Expt. Sta. Bui. 183: 

7-46. 1918. 
Ames, Adeline The temperature relations of some fungi causing storage rots. 

Phytopathology 5: 11-19. 1915. 
Askenasy, E. Ueber einige Beziehungen zwischen Wachsthum und Temper- 

atur. Ber. Deut. Bot. Ges. 8: 61-94. 1890. 
Balls, W. S. Temperature and growth. Ann. Bot. 22: 557-591. 1908. 
Brooks, Charles, and Cooley, J. S. Temperature relations of apple-rot 

fungi. Jour. Agr. Research 8: 139-164. 1917. 
Duff, George H. Some factors affecting viability of urediniospores of Cro- 

nartium ribicola. Phytopathology 8: 289-292. 1918. 
Edgerton, C. W. Effect of temperature on Glomerella. Phytopathology 5: 

247-259. 1915. 
Edgerton, C. W. Effect of temperature on Glomerella. Science n. s. 41: 174. 

1915. 
Eriksson, J. Ueber die Forderung der Pilzsporenkeimung durch Kalte. 

Centb 1 . f. Bakt. II 1: 557-565. 1895. 
Fromme, F. D. The culture of cereal rusts in the greenhouse. Bui. Torrey 

Bot. Club. 40: 501-521. 1913. 
Gilman, J. C. Cabbage yellows and the relation of temperature to its occur- 
rence. Ann. Missouri Bot. Gard. 3: 25-82. 1916. 
Hecke, Ludwig Untersuchungen tiber Phytophthora infestans De By. als 

Ursache der Kartoffelkrankheit. Jour. Landw. 46: 97-142. 1898. 
Johnson, E. C. Cardinal temperatures for the germination of uredospores of 

cereal rusts. Phytopathology 2: 47-48. 1912. 
Johnson, James Host plants of Thielavia basicola. Jour. Agr. Research 7: 

289-300. 1916. 



1919] Lauritzen: Infection Relations 35 

(15) Koeppen, W.P. Warme und Pflanzenwachsthum. Bui. Soc. Imp. Nat.Moscou 

43,1870:41-110. 1871. 

(16) Lehenbauer, P. A. Growth of maize seedlings in relation to temperature. 

Physiological Research 1 : 247-288. 1914. 

(17) Levin, Ezra The leaf-spot disease of tomato. Michigan Agr. Expt. Sta. Tech. 

Bui. 25:1-51. 1916. 
(IS) Livingston, B. E. The vapor tension deficit as an index of the moisture 
condition of the air. Johns Hopkins Univ. Cir. 293:170-175. March, 
1917. 

(19) Lock, R. H. On the growth of giant bamboos with special reference to the re- 

lation between conditions of moisture and the rate of growth. Ann. of 
Roy. Bot. Gard., Peradeniya 2: 211-267. 1904. 

(20) Mains, E. B. The relation of some rusts to the physiology of their hosts. 

Amer. Jour. Bot. 4: 179-220. 1917. 

(21) Melhus; I. E. Germination and infection with the fungus of the late blight 

of potato. Wisconsin Agr. Expt. Sta. Research Bui. 37: 1-64. 1915. 

(22) Pederson, R. Haben Temperaturschwankungen als solche einen ungiinstigen 

Einfluss auf das Wachsthum? Arb. Bot. Inst. Wiirzburg 1: 563-583. 
1874. 

(23) Price, H. L. The application of meterological data in the study of physiologi- 

cal constants. Ann. Rpt. Virginia Agr. Expt. Sta. 1909/10: 206-212. 1911. 

(24) Ravaz, L. and Verge, G. Influence de la temperature sur la Germination des 

conidies du mildiou. Prog. Agr. et Vit. 57: 170-177. 1912. 

(25) Ravn, F. Kolpin Nogle Helminthosporium-Arter og de af dem fremkaldte 

Sygdomme hos Byg og Havre. Bot. Tidskr. 23: 101-322. 1900. 

(26) Sachs, J. Textbook of botany. Translated by Alfred W. Bennett assisted by 

W. T. Thistleton-Dyer. Oxford, 1875. 

(27) Shapovalov, Michael Effect of temperature on germination and growth of 

the common potato-scab organism. Jour. Agr. Research 4: 129-133. 1915. 

(28) Shibata, K. Beitrage zur Wachstumsgeschichte der Bambusgewachse. Jour. 

of Sci. Imp. Univ., Tokyo 13: 329-496. 1900. 

(29) Tisdale, W. H. Relation of temperature to the growth and infecting power of 

Fusarium lini. Phytopathology 7: 356-360. 1917. 

(30) True, R. H. On the influence of sudden changes of turgor and of tempera- 

ture. Ann. Bot. 9: 365-402. 1895. 

(31) Wiesner, Julius Untersuchungen liber den Einfluss der Temperatur auf die 

Entwicklung des Penicillium glaucum. Sitzber. Akad. Wiss. (Vienna) 
Math. Naturw. Kl. 68: 5-16. 1874. 



